Self-monitoring battery operated circuit

ABSTRACT

Time pulse generator having biasing means therefor including a control device, which may be a transistor and means interconnecting the biasing means to the battery being monitored. The output of the time pulse generator is utilized to drive a signaling device to indicate a low level of battery energy and/or an alarm condition as detected by an external condition sensor.

The immediate application is for reissue of United States letters PatentNumber 3,778,800 granted December 11, 1973, on application Serial Number132,690 filed April 9, 1971. .Iaddend.

This application .[.is a continuation in part of.]. .Iadd.includessubject matter disclosed in part in .Iaddend.U.S. Pat. Ser. No. 876,156,filed Dec. 4, 1969, .Iadd.now Pat. No. 3,735,375 .Iaddend.which is astreamlined continuation of U.S. Pat. Ser. No. 546,663 filed May 2,1966, .Iadd.abandoned, .Iaddend.for "Circuit for Detection of SmallChanges in Conductors of High Resistance."

The present invention relates to battery operated electronic deviceshaving means for sensing and indicating low levels of battery energy.

Development of the solid state electronic art has advanced to the pointwhere amplifying and control devices can be made to draw extremely smallcurrent when fully turned on, and when turned off they draw such a verylow current that for all practical purposes they can be said to drawzero current. These properties are largely responsible for the increaseduse of battery operated solid state circuits because battery life cannow be extended to such a degree that even circuits calling for a highdegree of reliability can be utilized for battery operation. This latertype of circuit would include, among others, those designed formonitoring and detection functions, where quiescent power consumptioncan be made extremely small and where higher power drain circuitperformance, while very critical from a reliability standpoint, isnevertheless a fairly infrequent occurrence.

Although battery life can be made to extend for periods of severalyears, for low power consumptive circuits, it is nonetheless desirableto have available a sure and effective means for determining batteryenergy level so that batteries may be replaced before there is anydanger that the circuit will fail to operate because of power failure.It is desirable to have supervision of a parameter to be detected, suchas smoke, fire and the like, as well as the power supply for a period ofat least one year without attention or maintenance. During this periodthere should be provided a total of at least 25 novelty alarms of aduration of at least 2 minutes each. In addition, there should beprovided an extended trouble or battery monitor signal of at least 200hours duration plus 5 minutes of continuous alarm available during thetrouble period.

Prior art devices have used a supervisory battery as a reference tomonitor the condition of a battery used for power, however, if thesupervisory battery were to fail, no provision is made for registeringan alarm condition or for monitoring of the main battery which is anobvious deficiency.

It is thus the primary objective of this invention to provide a batteryenergy monoitoring circuit which drives its own power from the samesource as that being monitored and overcomes the deficiencies of theprior art devices.

A second object of the invention is to provide a battery energy levelmonitor which will produce its own alarm when the energy in the batterybeing supervised is reduced to some predetermined level.

A further object of the invention is to provide a battery operated lowpower consumptive detector and alarm device which comprises a batteryenergy level monitor utilizing the same alarm means as that forindicating a true alarm.

A still further and general object of the invention is to improve thereliability of battery powered circuits.

Other objects, features and advantages of the invention will becomeapparent upon a reading of the following detailed description of apreferred form of the invention as it appears in combination with acircuit for detecting fire or products of combustion.

FIG. 1 is a block diagram of the invention in combination with aproducts of combustion detector.

FIG. 2 is a schematic diagram of a preferred form of the circuit of theinvention in combination with typical fire detector unit, similar inoperation and construction to those fire and products of combustiondetectors disclosed in copending U.S. Pat. application Ser. No. 876,156,filed Dec. 4, 1969, which is a continuation of U.S. Pat. Ser. No.546,663, filed May 2, 1966 .[.and of which this application in acontinuation-in-part.]..

The preferred form of the invention includes generally a transducer 3, aDC amplifier 5, a time pulse generating circuit 7, the battery energylevel monitor 9, and the alarm means 11, as shown combined in the blockdiagram of FIG. 1.

In order to provide for longevity of battery operated systems upon theindication of an alarm condition, it is desirable that the alarm meansbe powered intermittently as opposed to a continuous time operation ofthe horn, light or whatever other means is employed to call attention tothe alarm condition. Likewise, the means for indicating low batteryenergy must itself conserve power and yet be able to provide a batterylevel alarm signal for a period of at least 24 hours. This latter powerrequirement also indicates the advisability of a pulsed alarm system.

Having the foregoing power limitations in mind, it will be noted at theoutset that the operation of the detector and battery monitor is soarranged that the pulse time generating circuit 7 produces no pulsetrain output when the input to the DC amplifier 5 is zero. Generation ofan input signal to the amplifier 5 will result in a pulse train outputwhich excites the alarm means in conformance with pulse spacing. As theinput signal increases in magnitude, the pulse spacing decreases and thealarm indication becomes more intense. If desired, the pulse timegenerating circuit 7 can be made to eliminate all spacing betweenpulses, and thus produce a continuous output voltage for short periodsof time when the condition being detected is most severe, as is theinstance of a smoke detection circuit where the smoke density becomeshigh.

Output from the battery energy monitor circuit will also result in thegeneration of a pulse train from the time pulse generating circuit 7;however, the pulse spacing is preferably made relatively long so as toachieve the object of power conservation during a battery conditionalarm.

An embodiment of the FIG. 1 concept is shown in FIG. 2 where thetransducer takes the form of an ion chamber 14 of the type having twospaced electrodes defining a gas containing space therebetween and alsoincluding a radioactive radiation source 14a. The ion chamber and itscharacteristics are more elaborately treated in the disclosures of saidprior U.S. Pat. applications, Ser. Nos. 546,663 and 876,156, and willtherefore not be described in further detail here.

An insulated gate field effect transistor 16, an amplifier transistor17, and an SCR amplifier switch 22, together with their related sourceof power and biasing circuits, comprise the DC amplifier portion of thesystem. The power source is found in batteries 18, 19 and 20 which areconnected in series in a manner well known to the art in order toprovide proper division of voltage for the various elements of thecircuit.

The time pulse generating circuit 7 includes a pulse feedback capacitor24 with appropriate interconnections between the DC amplifier (at thecollector of transistor 17) and the battery monitoring device, shown astransistor 26, as will more fully appear subsequently.

In clear air operation, the ion chamber 14 draws sufficient currentthrough the high resistance R₁ that the field effect transistor 16 isheld on. As smoke or other products of combustion enter the open ionchamber 14, the resistance of the chamber increases, causing the fieldeffect transistor 16 to turn off. Series connected resistors R₂, R₃ andR₄ are of such values as to provide proper voltage at the wiper 29 of R₃to turn on the first amplifier transistor 17 at such time as the fieldeffect transistor 16 starts to turn off. As transistor 17 turns on fromits normal off state, a voltage arises on the collector of thetransistor which point is connected to the gate of the SCR amplifierswitch 22. Application of this voltage turns the SCR on and the currentconducted therethrough also flows through and activates an alarm horn 30which is connected in series with the SCR 22. The SCR 22 and horn 30 areconnected across the batteries 18, 19 and 20 which provide power fortheir operation.

When the SCR switch 22 turns on, the pulse feedback capacitor 24 isdischarged, and provides a signal to the base of the transistor 26through a resistor R₅, turning off the transistor 26 and theinterrupting the path to the drain of the field effect transistor 16.With this interruption, the field effect transistor 16 turns furtheroff, thus turning on transistor 17, the SCR 22 and the horn 30. Whencapacitor 24 is fully discharged, transistor 26 turns on, turning FET 16on, turning transistor 17 off. When the transistor 17 is turned off, thecapacitor 24 charges, restoring the voltage to the base of transistor 26and, if smoke is still present in the ion chamber, the process repeatsitself, resulting in intermittent operation of the horn 30.

Without the previously discussed regard for power consumption duringalarm, it is possible to arrange the bias voltages and other parametersof the circuit so that a high smoke density in the ion chamber will turnoff the transistor 16 to such an extent that the feedback signal, fromthe capacitor 24, has no further effect since the transistor 16 isalready turned off and the horn will sound continuously.

The transistor 26, previously referred to in connection with the pulsefeedback circuit, acts also as the fundamental part of the batteryenergy detector. With fully charged batteries, there exists a voltage ofapproximately one-half volt on the base of transistor 26, this voltageappearing at the juncture of R₆ and R₇, a voltage divider connectedacross the batteries being monitored. The one-half volt maintainstransistor 26 in an on state and provides a path from the drain sourceof the field effect transistor 16 so that it may function.

As such time as the energy of batteries 18, 19 and 20 is reduced to thepoint where the voltage divider comprising R₆ and R₇ suppliesapproximately .4 volts or less to the base of transistor 26, transistor26 starts to turn off, impeding the drain source path of transistor 16.As transistor 26 turns off, the gate-to-source voltage in transistor 16increases, tending to turn transistor 16 off in the same fashion as withsmoke particles in the ion chamber. Also in the same manne as with atrue alarm, the horn 30 is turned on briefly and then turned off throughthe feedback action of the capacitor 24. It should be noted that lowbattery voltage turns the transistor 26 only partially off while afeedback pulse through the capacitor 24 will turn it off definitively.Thus, it will be noted that the alarm signal and the monitor signal arequite distinctive, one from the other. The alarm signal provides rapidintermittent occurring signals with a minimum of time between signalsincreasing to a continuous signal as the severity of the alarm conditionincreases. The monitor alarm signal, on the other hand, occurs for onlyshort intervals with relatively long periods between signals, however,it is noted that an alarm signal will override the monitor signal andwill take precedence thereover if an alarm condition develops even afterthe monitor signal has been activated.

The practical result of the battery detection circuit is to produce veryshort monitor alarm sounds at widely spaced intervals as the batterystarts to lose significant energy, but as more energy is lost and as thebattery voltage drop continues, the monitor alarm becomes more frequentor in other words, the periods between monitor alarm signals becomesshorter.

What is claimed is:
 1. Battery operated electronic detection apparatus,comprising:a set of electrical terminals for connection to the terminalsof a battery power source; battery powered means for sensing a selectedcondition .Iadd.external to said apparatus .Iaddend.and generating afirst electrical signal representative of said condition, said sensingmeans being connected to receive power from said electrical terminalswhereby to be powered by .[.a.]. .Iadd.said .Iaddend. battery powersource connected thereto, .Iadd.a common portion of .Iaddend.saidsensing means also being responsive to the output voltage of .[.the.]..Iadd.said .Iaddend. battery power source connected to said electricalterminals to generate a second electrical signal whenever said outputvoltage falls below a predetermined level; and, battery powered alarmmeans .Iadd.including only a single alarm giving device .Iaddend.connected to receiver power from said electrical terminals whereby to bealso powered by .[.the.]. .Iadd.said .Iaddend.battery power sourceconnected thereto, said alarm means being connected to said .Iadd.commonportion of said .Iaddend.sensing means to be driven by either said firstor second electrical signal and being operable to generate .[.an.]..Iadd.a respective .Iaddend.alarm signal corresponding to .Iadd.andindicating .Iaddend.the .Iadd.particular .Iaddend.electrical signal bywhich it is driven.
 2. The invention defined in claim 1 wherein:saidselected condition sensed by said sensing means is the clarity of air;and, said sensing means includes ion chamber means for sensing airclarity, said ion chamber means being operable to control current flowtherethrough as a function of the clarity of the air being monitoredtherein.
 3. The invention defined in claim 2, wherein said sensing meansincludes a field effect transistor, said sensing means being operable togenerate said first and second electrical signals by controlling thecurrent flow through the drain-source current path of said field effecttransistor as a function of, respectively, the intensity of saidselected condition being sensed and the level of the output voltage ofthe battery power source connected to said electrical terminals.
 4. Theinvention defined in claim 3, wherein said sensing means includes:sensormeans for sensing said selected condition and generating an electricalcontrol signal corresponding thereto, the gate electrode of said fieldeffect transistor being connected to receive said control signal wherebythe electrical resistance of the drain-source current path of said fieldeffect transistor varies as a function of the magnitude of said controlsignal; and, a first transistor having its emitter-collector currentpath connected as current control device in series with saiddrain-source current path, the base electrode of said first transistorbeing connected to monitor the output voltage of the battery powersource connected to said electrical terminals whereby to control thecurrent flow through said series connected emitter-collector anddrain-source current paths as a function of the level of said outputvoltage.
 5. The invention defined in claim 4, wherein:said alarm meansincludes a horn connected in series with the anode-cathode current pathof a silicon controlled rectifier; and including: resistor means havinga voltage pickoff connected in series with the drain-source current pathof said field effect transistor whereby to generate a voltage signal onsaid voltage pickoff proportional to the current flow through saiddrain-source current path; and, a second transistor connected as anamplifier between said voltage pickoff and the gate electrode of saidsilicon controlled rectifier said second transistor being operable togenerate and apply said first and second electrical signals to saidcontrol electrode by amplifying the voltage signal appearing on saidvoltage pickoff.
 6. The invention defined in claim 5, including acapacitor connected between the control electrode of said siliconcontrolled rectifier and the base electrode of said first transistor,said capacitor being discharged through said silicon controlledrectifier whenever the anode-cathode current path of said siliconcontrolled rectifier is triggered into conduction by the generation ofeither said first or second electrical signal on said control electrode,the discharge of said capacitor being operable to apply a feedback pulseto the base electrode of said first transistor which biases theemitter-collector current path of said first transistor into asubstantially nonconductive state.
 7. The invention defined in claim 1,wherein said first and second electrical signals generated by saidsensing means are distinctly different so that the alarm signalgenerated by said alarm means in response to said first electricalsignal is noticeably different from the alarm signal generated inresponse to said second electrical signal.
 8. The invention defined inclaim 7, wherein:said first electrical signal is a first pulse trainhaving a pulse spacing inversely proportional to the intensity of saidselected condition being sensed; and, said second electrical signal is asecond pulse train having a pulse spacing noticeably greater than thepulse spacing of said first pulse train and a pulse width noticeablyshorter than the pulse width of said first pulse.
 9. Battery poweredelectronic detection apparatus, comprising:a set of electrical terminalsfor connection to the terminals of a battery power source; batterypowered first means for sensing a selected condition .Iadd.external tosaid apparatus .Iaddend.and generating a first electrical signalrepresentative of said condition, said first means being connected toreceiver power from said electrical terminals whereby to be powered by.[.a.]. .Iadd.said .Iaddend.battery power source connected thereto;battery powered second means responsive to the output voltage of.[.the.]. .Iadd.said .Iaddend.battery power source connected to saidelectrical terminals for generating a second electrical signal wheneversaid output voltage falls below a predetermined level, said second meansbeing connected to receive power from said electrical terminals wherebyto be also powered by .[.the.]. .Iadd.said .Iaddend.battery power sourceconnected thereto; and, battery powered alarm means .Iadd.including onlya single alarm giving device .Iaddend.connected to receive power fromsaid electrical terminals whereby to be powered by .[.the.]. .Iadd.said.Iaddend.battery power source connected thereto, said alarm means.Iadd.device .Iaddend.being connected to .Iadd.a common portion of.Iaddend.said first and second means to be driven by either said firstor second electrical signal and being operable to generate .[.an.]..Iadd.a respective .Iaddend.alarm signal corresponding to .Iadd.andindicating .Iaddend.the .Iadd.particular .Iaddend.electrical signal bywhich it is driven. .Iadd.
 10. Apparatus as defined in claim 1 whichfurther includes means for effecting pulsation of said alarm meansdevice when driven by said second electrical signal. .Iaddend..Iadd. 11.Apparatus as defined in claim 10 in which the frequency of pulsation ofsaid alarm means device increases in proportion to the amount of fall ofsaid output voltage below said predetermined level. .Iaddend. .Iadd. 12.An electronic detection apparatus adapted to be powered from theterminals of a single source of battery power, said electronic detectionapparatus comprising: a set of electrical terminals connected to theterminals of said source of battery power; first means for sensing aselected condition external to said apparatus and generating a firstelectrical signal representative of said condition; second means forgenerating a second electrical signal whenever the output voltage ofsaid source of battery power falls below a predetermined level; alarmmeans connected to said first and second means and responsive to eithersaid first or said second electrical signal to generate an alarm signalindicating which of said first and second electrical signals it isresponding to; and, means connecting said first and said second meansand said alarm means to said set of electrical terminals whereby saidfirst and said second means and said alarm means are all powered only bysaid single source of battery power through said set of electricalterminals..Iaddend..Iadd.
 13. An electronic detection apparatus asclaimed in claim 12 wherein said first and said second means includecommon circuit means common to said first and said second means andthrough which said first and second electrical signals are generated,said alarm means being connected to said common circuit means..Iaddend..Iadd.
 14. An electronic detection apparatus comprising: a setof electrical terminals adapted for connection to the terminals of abattery power source; first means for sensing a selected conditionexternal to said apparatus and generating a first electrical signalrepresentative of said condition; second means for generating a secondelectrical signal whenever the output voltage of said battery powersource falls below a predetermined level; alarm means connected to saidfirst and second means and responsive to said first or said secondelectrical signal to generate an alarm signal indicating which of saidfirst and second electrical signals it is responding to; and, meansconnecting said first and said second means and said alarm means to saidset of electrical terminals whereby said first and said second means andsaid alarm means are all powered by said battery power source; saidfirst and said second means including common circuit means common tosaid first and said second means and through which said first and saidsecond electrical signals are generated, said alarm means beingconnected to said common circuit means. .Iaddend..Iadd.
 15. Anelectronic detection apparatus as claimed in claim 14 wherein saidcommon circuit means includes at least one active circuit element forgenerating said first and second electrical signals, said alarm meansbeing connected to the output of said active circuit element..Iaddend..Iadd.
 16. An electronic detection apparatus as claimed inclaim 15 wherein said active circuit element is a semiconductor device..Iaddend..Iadd.
 17. An electronic detection apparatus as claimed inclaim 14 wherein said common circuit means includes first amd secondactive circuit elements connected to each other and through which saidfirst and said second electrical signals are generated, said alarm meansbeing connected to one of said active circuit elements. .Iaddend..Iadd.18. An electronic detection apparatus as claimed in claim 17 whereinsaid first and second active circuit elements are semiconductor devices..Iaddend..Iadd.19. An electronic detection apparatus as claimed in claim14 wherein said common circuit means includes first, second, and thirdactive circuit elements through which said first and said secondelectrical signals are generated, said first and said third activecircuit elements being connected to said second active circuit elementand said alarm means being connected to said first active circuitelement. .Iaddend..Iadd.
 20. An electronic detection apparatus asclaimed in claim 19 where said first, second and third active circuitelements are all semiconductor devices. .Iaddend. .Iadd.
 21. Anelectronic detection apparatus adapted to be powered from the terminalsof a single source of battery power, said electronic detection apparatuscomprising: a set of electrical terminals connected to the terminals ofsaid source of battery power; first means for sensing a selectedcondition external to said apparatus and generating a first electricalsignal representative of said condition; second means for generating asecond electrical signal whenever the output voltage of said source ofbattery power falls below a predetermined level; alarm means connectedto said first and second means and responsive to either said first orsecond electrical signal to generate an alarm signal indicating which ofsaid first and second electrical signals it is responding to; and, meansconnecting said first and said second means and said alarm means to saidset of electrical terminals whereby said first and said second means andsaid alarm means are all powered only by said single source of batterypower through said set of electrical terminals;said alarm meansincluding a single alarm device, said single alarm device beingresponsive to said first electrical signal for generating a first alarmsignal and said single alarm device being responsive to said secondelectrical signal for generating a second alarm signal that is distinctfrom said first alarm signal. .Iaddend..Iadd.
 22. An electronicdetection apparatus adapted to be powered from the terminals of a singlesource of battery power, said electronic detection apparatuscomprising:a set of electrical terminals connected to the terminals ofsaid source of battery power; first means for sensing a selectedcondition external to said apparatus and generating a first electricalsignal representative of said condition; second means for generating asecond electrical signal whenever the output voltage of said source ofbattery power falls below a predetermined level; alarm means connectedto said first and second means and responsive to either said first orsaid second electrical signal to generate an alarm signal indicatingwhich of said first and second electrical signals it is responding to;and, means connecting said first and said second means and said alarmmeans to said set of electrical terminals whereby said first and saidsecond means and said alarm means are all powered only by said singlesource of battery power through said set of electrical terminals; saidalarm means comprising a single alarm device and a switch meansconnected together in series between the electrical terminals of saidset of electrical terminals, said switch means being responsive to saidfirst and said second electrical signals for controlling current flowthrough said single alarm device. .Iaddend. .Iadd.
 23. An electronicdetection apparatus as claimed in claim 22 wherein said single alarmdevice comprises: means emitting an audible sound; said first meanscomprises means producing, as said first electrical signal, a firstsequence of electrical pulses at a first repetition rate; and saidsecond means comprises means producing, as said second electricalsignal, a second sequence of electrical pulses at a second repetitionrate. .Iaddend..Iadd.
 24. An electronic detection apparatus as claimedin claim 23 wherein said first repetition rate varies as the severity ofsaid condition varies. .Iaddend.